This invention relates to a semiconductor light emitting device made by using nitride semiconductors or the like, its manufacturing method, and a connection structure of an electrode layer. More particularly, the invention relates to a semiconductor light emitting device of the type that reflects light generated in the active layer with an electrode layer deposited on the active layer, its manufacturing method, and a connection structure of the electrode layer.
Gallium nitride-family compound semiconductors are increasing their use as semiconductor materials for visible light emitting devices, and their development is progressing especially in the field-of blue and green light emitting diodes. Light emitting diodes, in general, have a structure of sequential deposition of n-type semiconductor layers, active layers and p-type semiconductor layers by crystal growth of gallium nitride-family compound semiconductor layers on a sapphire substrate, or the like. In case of a light emitting diode having this kind of multi-layered structure, electric current is introduced to the active layer, and light generated in the active layer is externally taken out.
In regard to semiconductor light emitting devices of this type, there are known structures configured to extract light traveling upward of the active layer and structures configured to extract light traveling downward of the active layer through a transparent substrate. Among such structures configured to extract light through a transparent substrate, there is a device having a structure using an electrode connected to a p-type semiconductor layer as a reflective layer. For example, a light emitting diode device disclosed in Japanese Patent Laid-Open Publication No. hei 11-191641, a light emitting diode device disclosed in Japanese Patent Laid-Open Publication No. hei 11-220170 and a semiconductor light emitting device disclosed in Japanese Patent Laid-Open Publication No. 2000-91638 are known among others.
In such devices configured to reflect light emitted in a semiconductor light emitting device at a p-side electrode interface, since light reflected by the p-side electrode interface is added to the light traveling through the substrate as the output light through the substrate, the emission efficiency of the light emitting devices can be enhanced. As to a device described in Japanese Patent Laid-Open Publication No. hei 11-191641 and a semiconductor light emitting device described in Japanese Patent Laid-Open Publication No. 2000-91638, there are disclosed structures forming a contact metal layer for ohmic contact between a p-type semiconductor layer and an electrode layer functional as a reflective layer.
However, even in case a contact layer is formed for the purpose of ensuring reliable contact with the p-side semiconductor layer, if the thickness of the contact layer is as thick as approximately 50 nm, for example, it is difficult to enhance the reflectance, and it needs improvement of the reflection structure itself, including the contact metal layer under the demand for higher and higher light emitting efficiency.
It is therefore an object of the invention to provide a semiconductor light emitting device and its manufacturing method capable of realizing higher emission efficiency and to provide a connection structure of an electrode layer capable of realizing higher efficiency.
A semiconductor light emitting device according to the invention including a semiconductor light emitting layer of a first conduction type, an active layer and a semiconductor layer of a second conduction type which are sequentially deposited on an optically transparent substrate, comprises: an electrode layer formed on the semiconductor layer of the second conduction type on the active layer, and a contact metal layer interposed between the electrode layer and the semiconductor layer of the second conduction type and adjusted in thickness not to exceed the intrusion length of light emitted generated in the active layer.
With the above-summarized semiconductor light emitting device, since the semiconductor layer of the first conduction type, active layer and semiconductor layer of the second conduction type are sequentially stacked, the active layer can generate light with a current injected therein. Since the substrate is optically transparent, the light generated in the active layer is radiated through the substrate, but part of the light generated in the active layer travels toward the semiconductor layer of the second conduction type. Since the electrode layer overlies the semiconductor layer of the second conduction type, their interface can reflect the light traveling toward this semiconductor layer. Thus the light traveling toward the semiconductor layer of the second conduction type is reflected toward the substrate. Since the contact metal layer is interposed between the electrode layer-and the semiconductor layer of the second conduction type and adjusted in thickness not to exceed the intrusion length of the generated light, reflectance by .the electrode layer can be enhanced while the ohmic contact is ensured, and the emission efficiency of the entire device can be enhanced accordingly.
A method of manufacturing a semiconductor light emitting device according to the invention comprises the steps of: sequentially depositing a semiconductor light emitting layer of a first conduction type, an active layer and a semiconductor layer of a second conduction type on an optically transparent substrate; forming a contact metal layer on the semiconductor layer of the second conduction type, which is adjusted in thickness not to exceed the intrusion length of light generated in the active layer; and forming an electrode layer on the contact metal layer.
In the above-summarized manufacturing method of a semiconductor light emitting device, the contact metal layer adjusted in thickness not to exceed the intrusion length of the light generated in the active layer after the semiconductor layer of the second conduction type is formed, and the electrode layer is formed after the contact metal layer having that thickness is formed. Therefore, the contact metal layer having the thickness not exceeding the intrusion length of the light generated in the active layer can enhance the reflectance by the electrode layer while the ohmic contact is ensured, and the intensity of reflection toward the optically transparent substrate can be enhanced accordingly.
A connection structure of an electrode layer according to the invention comprises: an optically transparent semiconductor layer; a contact metal layer formed on the semiconductor layer and adjusted in thickness not to exceed the intrusion length of light passing through the semiconductor layer; and an electrode layer formed on the contact metal layer. With this connection structure of the electrode layer, similarly to the semiconductor light emitting device, since the contact metal layer is interposed between the electrode layer and the semiconductor layer and adjusted in thickness not to exceed the intrusion length of the generated light, reflectance by the electrode layer can be enhanced while the ohmic contact is ensured.